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EMSS - ECF Metal tubemods Safety Specification

Discussion in 'Announcements and News' started by rolygate, Feb 23, 2012.

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  1. rolygate

    rolygate Forum Manager Verified Member ECF Veteran

    Supporting member
    Sep 24, 2009
    ECF Towers
    What this is
    A set of design and manufacturing features that in our opinion ensure that APVs of a certain type - metal tubemods - cannot explode.

    EMSS applies only to metal tubemods. We will not consider stating that devices which do not comply with the full requirements of EMSS are 'safe' as in our opinion only those devices that fully comply can be so described.

    In practice, no device can realistically be described as 'safe' because they all use lithium ion cells, and in our opinion these are intrinsically unsafe. However by full implementation of the EMSS requirements, a device is in our opinion acceptably safe.

    The EMSS by its nature classifies devices as either passing or failing. It may be the case that a standards and testing organization could allocate different grades of safety, e.g. gold/silver/bronze pass grades. ECF does not have the facilities to offer this type of service.

    All issues of this type are purely a matter of opinion and there is no scientific basis at this time for any opinions expressed by anyone.

    Why ECF is doing this
    Some metal tube APVs that can have two batteries fitted have exploded causing facial injury to the user. No other APVs or e-cigarettes of any kind are affected.

    ECF has been warning about this issue for exactly two years in March 2012. The first warnings were given in March 2010, and the first version of our safety guidelines - EMSS v1 - came out in March 2011, one year ago. Neither the warnings nor the EMSS are new. What is new is that situation now calls for increased prevalence of warnings to buyers. The EMSS is now mature at v2 and suitable for much wider promotion.

    Both newcomers and experienced vapers have suffered injury as a result of explosions. Although user error can be responsible - for example, by mistake charging standard (non-rechargeable) batteries and using them in the device - it may be that the problem is exacerbated by the wide availability of counterfeit batteries. Because of this, it is impossible for users to guarantee what batteries are being used. Therefore, even when correctly purchased and used precisely as directed, it may be possible for a metal tube APV to explode and cause injury.

    As a result, APVs need to be able to cope with batteries failing, since what appear to be top-quality batteries could instead be fakes: reject unprotected Li-ion cells that have been bought cheaply as bulk reject stock, stripped, and recovered with a fake label.

    The exploding ecig issue is now international news. It has begun to be used as a reason to ban e-cigarettes. We foresee this situation getting worse unless something is done about it. The unfortunate fact is that what you do in the privacy of your home has implications that go way beyond your front door: when you are taken by ambulance to hospital, and when the fire service are present for hours at the home, and when they decide to carry out an investigation, and when the police also carry out an investigation, and when it is widely reported in the media - perhaps you can see that it affects the rest of us.

    The EMSS provides a list of desirable safety features and is the minimum set that, in the opinion of ECF, is likely to provide some guarantee of preventing an explosion. More safety features will increase the level of safety. The big advantage of this set of features is they can be fitted to any metal tubemod and they fix the problem.

    If compliant, a product can be described and advertised as 'EMSS Compliant' or similar - see Description below.

    __________________________________ _______________________________

    EMSS - ECF Metal tube APV Safety Specification v2

    The EMSS, and warnings to buyers, are only applicable to metal tube devices that can take two batteries either by design, or by user error, or by deliberate misuse, and where the device will function with two batteries inserted. The EMSS therefore refers to APVs that accept two batteries, or that accept an 18650, and could therefore have two smaller batteries inserted, and without electronic controls that prevent operation due to overvoltage. Some fully-electronic devices, that can accept two batteries, may therefore be exempt since they will not function.

    Any metal tube APV that can only accept one battery is exempt at this time.

    It does apply to metal tube devices that take one battery but for which an extender tube is available OEM (from the original manufacturer) to enable longer cells or two cells to be fitted.

    1. Three or more milled slots in the metal tube body
    Three (or more) gas vent slots to be fitted along the length of the tube body.
    For a standard APV taking 1 x 18650 cell or 2 x 16340 cells, the slots should be of 50mm x 4mm, or 2 inches x 5/32nds, and extend along the length of the body of the metal tube.
    Each slot to have a cross-sectional area of ~200mm2.
    If full-length 2" slots cannot be used then four slots should be fitted. The key is the total cross-sectional area of the gas vents.
    Where possible, consideration should be given to the relief of gas pressure both at the top and bottom of the tube. Pressure relief at the top end is considered much more important than at the bottom because (a) gas is vented from the top of a failing cell, and (b) a cell in meltdown can swell and block the tube, causing high pressure at the top end.
    A perforated metal tube body is also acceptable [1].

    2. An electrical or electronic fuse
    An electrical fuse could be a collapsible spring that melts fast under load (aka a 'hot spring').
    An electronic fuse could be an overcurrent trip.

    3. A separate master on/off switch
    A way to disconnect the battery in addition to the regular activation switch.
    A locking on/off switch is not as good but is acceptable.

    4. Designed for and sold with safer-chemistry or protected batteries
    A metal tube APV should be designed to use safer-chemistry cells such as Li-Mn or Li-FePo4 batteries, or protected Li-ion batteries.
    Where the batteries are supplied, it should be sold with those batteries.

    Important Note
    APVs should have an info sheet attached. This guide should state how the device can be used and not used. Batteries are an important part of this information: what cells must be used, and what charger. A warning not to use any other type of battery should be included (and especially not primary cells [regular batteries] or unprotected Li-ion cells such as RC123's). This type of guide and safety info is standard for all consumer products. Omitting this sheet (or manual) leaves a vendor open to action as it is a basic requirement. We suggest that the info sheet can be rolled and inserted in the device; or rolled around it and attached with an elastic band; or be placed at the top of the package such that the device cannot be used without seeing the info sheet or manual.

    In some circumstances, there may be good reasons to exempt a product from some provisions of EMSS, or to modify (reduce) the compliance requirements. Some examples are given below.

    1. A perforated tube such as the stainless tubes linked to at the bottom does not require gas vent slots assuming that the design chosen does not have minimal perforations and that the cross-sectional vent area exceeds 500mm2.

    2. A box section ('square tube') APV would not require distributed vents since it is unlikely that gas venting down the tube can be blocked by swollen batteries. A vent slot cross-sectional area reduced by 50% seems appropriate. Alternatively, gas vent holes of equal area might be appropriate, and these could probably be placed at any convenient point not in the centre of any of the four sides. We would need to confer with the designer on this.

    3. If a fully-electronic APV cannot operate with two batteries inserted then, at this point in time, we consider it exempt. In other words if it shuts down when supplied with >5 volts then it can be classed as a single-battery device and thus exempt.

    4. NC mills (computer controlled milling machines) have been shown capable of executing complex designs for slot formation, including art designs, or the brand name in slot form. Provided that (a) the cross-sectional area is sufficient and (b) the slots are distributed well so that potential high-pressure areas at the top and bottom of the tube are covered, such designs are acceptable. We would need to confer with the designer on this.

    5. Completely new APV designs with innovations such as internal vent channels (and provision for equalising the venting gas thrust directions so that a rocket-mode fail is not caused) may well be completely exempt from EMSS. An example of the new design must be presented for inspection in order to receive an exemption.

    One reason for the introduction of the specification was so that other, better designs are produced, as current designs are proving problematic with the new level of battery counterfeiting. Also, new types of battery could be investigated, since lithium cells cannot be regarded as intrinsically safe.

    Other exceptions may be allowed later.

    If listed by ECF as compliant, an APV may be described in advertising or promotion in the following terms.
    EMSS Compliant
    ECF Compliant
    ECF EMSS Compliant
    Complies With EMSS
    Complies With ECF EMSS
    Listed As Complying With EMSS

    Not Allowed:
    ECF Approved
    EMSS Approved
    ECF Tested

    ...or similar. This is because we have not inspected, tested and approved any product (and cannot). ECF cannot test and 'approve' any product, it is not a testing authority. We will list it as complying with EMSS.

    __________________________________ _______________________________

    Is it safe?
    If a metal tube APV has the above four features we would describe it as safe.

    It does not mean 'absolutely safe' as that cannot be; it means that an explosion in front of the face is very unlikely in our opinion. A battery can fail violently, as that is a separate issue, but it means that even if it does so, the failure should not cause an explosion.

    The single most important feature is the fitting of large gas vent slots, because with these in place an APV cannot explode and drive the top end or atomizer into the user's face. The other protections may or may not work, but an APV mod with well-distributed large holes in the body cannot fire the mouthpiece fitting into the user's face with force, and it cannot drive the device hard into the user's face as a result of a bottom end blowout plug working correctly.

    Additional safety features
    There are other measures that can be adopted to increase safety. If these are also present, the level of protection increases.

    - An internal battery isolation sleeve
    A non-conducting internal sleeve to prevent a battery with a tear on its outer cover shorting out to the metal body of the APV [2]. The sleeve would need to be perforated in order not to block the gas vent slots.

    Reverse polarity protection
    An electronic trip designed to cut out if the battery or batteries are inserted the wrong way round.

    Thermal trip
    An electronic or mechanical fuse that trips if it senses heat within the tube body.

    An isolated 2-wire circuit
    Best practice electrical design suggests that an ideal DC circuit consists of two insulated poles, and that a machine's external casing should not be used as one side of the circuit. It means both sides of the circuit are run in insulated cables, and isolated from the device body. This would be obvious in the case of AC but is not so clear when the circuit is low-voltage DC. Please note that a 2-wire insulated circuit has nothing at all to do with earthing a machine casing where that is needed - that is a separate issue.

    This is a theoretical requirement that is hard to use in practice (here), but raises the level of safety if it can be used. For most existing APVs it would require a complete re-design and is not practical. It is mentioned here because new products are being designed all the time, and it is possible that some manufacturers may find it of interest.

    It is likely that the higher incidence of events in metal tubemods compared to those in boxmods is due to the battery can (its casing) short-circuiting to negative. This cannot happen in a plastic or wooden device such as a boxmod, or in a metal device where both poles are isolated.

    The casing absolutely MUST NOT be used as a positive return path, as a battery short to earth will then be to positive, and result in a fire that cannot be prevented by a fuse. This means a battery should not be inserted in reverse even in a mechanical or electrical APV where it will still function normally when this is done - a dead short due to a torn battery cover will result in a potentially dangerous incident.

    What we know
    We have developed these safety features over time as a result of lessons learned in the field. Two things have become clear:
    • Explosions have only occurred in certain types of metal tube devices that had two batteries inserted
    • Small gas vent holes were found to be extremely useful as an early warning, but they do not stop an explosion (unless the casing is unusually strong and no has no weak points at all)
    Small gas vents are useful since they result in the hand being burnt during the first-stage outgas, causing the device to be dropped. However they do not have sufficient cross-section to vent the second-stage outgas that causes an explosion. This means additional venting is required.

    We think milled slots are a better solution than a blowout plug because they can be seen and verified, and they cannot fail. A screw-on or press-fit plug may or may not work, as it it may be attached too firmly; but slots will always work. In addition when slots are used, there will be no reaction thrust from a blowout plug ejection: where a blowout plug operated correctly, it was noted that the thrust created caused the APV to strike the face sharply and caused injury.

    In addition, slots are distributed along the length of the tube, and much more likely to be able to dump gas pressure at either end of the tube than holes at one end. High pressure at the top end needs to be prevented, which is difficult if the tube is blocked by swollen batteries. Incidents where the atomizer blew off were likely caused by high pressure at the top of the tube, perhaps due to swollen batteries blocking vents lower down. It should be noted that a blowout plug at the bottom end would not have prevented these incidents.

    ECF safety lead
    We have designed this feature set over time, with improvements added as a result of experience, and several manufacturers have followed our recommendations. We would prefer that this was not the case and instead, manufacturers developed safety features as a priority, instead of working exclusively on better performance while appearing not to apply the same effort to safety.

    Partly as a result of our suggestions, and partly because single-battery VV mods have become popular, the number of APV explosions per thousand units sold (of all types of mods) has actually decreased. However, as the number of units sold in total has increased exponentially, these incidents may in fact be more frequent now. This latest update to our safety specification series is an attempt to reduce this trend.

    What is the purpose of the EMSS?
    To stop a metal tubemod exploding in the face of a user.

    Other considerations cannot be covered by this feature set - it is solely designed to stop the device exploding in the user's face, and does not address other issues such as meltdowns in use or while in a pocket or purse. The safety features should help to reduce the number of these, but it is not a prime consideration.

    The main requirement is to stop the APV casing fragmenting violently, or the mouthpiece end firing into the user's face, during an incident while in use. If neither of these can occur then the Safety Specification has succeeded in its primary task.

    Drawbacks of the Safety Features
    Everything has pros and cons - nothing is all benefit with no downside. Some negatives we can see are:
    - It will add to the cost of the product
    - In the event of an energetic 2-cell battery failure occurring in use, the hand that is holding the device is likely to be burnt before the unit is dropped

    As regards cost, this will apply equally to all manufacturers, so in the end there is a level playing field. We will promote APVs with EMSS as safer because that is inarguable - if it cannot explode or fire off the atomizer then it must be safer. Therefore, there will be a marketing advantage to having the safety features.

    Burns are probably inevitable - but preferable to an explosion in the face. There is no practical alternative that we can see. Blowout plugs are not as good an option for several reasons, including the fact they have resulted in injury to the user when they worked correctly. There is probably no ultimate safety feature of this type, that will absolutely prevent an explosion, without some kind of drawback.

    In case of an outgas, we expect that the device will be rapidly dropped, preventing any further injury from the hot gas. In all reports received of events where the APV had small gas vent holes, there was a low-level first-stage outgas that lasted several seconds, before the second-stage fierce outgas. We expect that the unit will be dropped during the first-stage outgas as it will probably be impossible to hold it. Some blisters on the hand are preferable to a severely damaged face or a child struck by a blowout plug moving with enough speed to damage an oak door as was noted in one incident of this type.

    General guidance
    Statistically, a single-cell VV APV is the safest way to obtain high voltage, because none has ever exploded. All explosions have been in 2-cell metal tubemods, therefore these need more attention to safety issues. A 2-battery device with the EMSS safety specification fully implemented can be regarded as being as safe as a 1-battery mod, since it is highly unlikely to explode.

    Unprotected Li-ion cells
    This is not recommended even in devices with multiple protections. Unprotected Li-ion batteries are proven dangerous and in our opinion there is no safe operational mode for these cells. The only possible reason to use them is economy. If you are selecting batteries to use in a 2-cell device for their cheap cost then by definition you are not taking safety issues seriously.

    One important reason why unprotected Li-ion cells are not safe is because they can be damaged while charging. If the charger is faulty, the batteries have no protection to prevent damage. The damaged and therefore faulty cells can then be fitted into an APV, by an unwary user.

    In our opinion the deliberate use of a pair of unprotected Li-ion batteries in a metal tubemod involves taking unnecessary risk even when the device complies with EMSS. This is due to the increased risk of an energetic failure, and therefore of burns to the hand even if no explosion takes place. Please do not use stacked unprotected Li-ion cells.

    Batteries with a C Rating too low
    Batteries are sold by their manufacturer as suited to a given maximum output current. Whatever type of cell is involved, it cannot be safe practice to overdrive them. The maker gives their max output for a reason.
    • In a single-battery VV device, the battery will need to supply about 4 or perhaps even 5 amps (in order to create a voltage higher than the cell voltage, for an atomizer needing 1.5 to 3 amps). It can be seen that a cell with a C Rating below this figure is not a good choice.
    • In a two-battery device, the batteries will need to supply about 1.5 to 3 amps (varies according to electronic or non-electronic operation). Cells with a C Rating below this figure are not a good choice.
    If in doubt use an AW 'red' Li-Mn battery. There are other safe choices, but we know these can do the job, and even better, you can buy them from an approved main distributor and therefore have a reasonable expectation they are of genuine manufacture. They are not cheap but you have to decide what price to put on your safety - in the end, it's your choice.

    Note that no lithium cells of any type are 'safe' - they cannot be. All will meltdown with heat and flames if abused. AW red cells have never been known to outgas so violently that an APV exploded, though, and that is all we are considering here.

    Single-battery metal tubemods
    Several metal tube APVs are sold that appear to have no realistic gas venting facility. These devices may in some cases be virtually gas-tight. There is an argument that this is of no concern because no single-cell mod has ever exploded. This is true, but:
    • Just because something has never happened does not mean that it will not happen one day. A gas-tight metal tubemod is potentially dangerous
    • Many of these units can have two batteries inserted for high-voltage vaping
    We know that this happens even when the manufacturer warns against it. This results in obvious danger. If an APV explodes then it is no help that it was used contrary to the maker's instructions, this will make no difference to the health of the individual involved or to the media reporting on it.

    All metal tubemods need to be made so that they cannot explode. User error, faulty batteries, misuse, charger issues and unsatisfactory design, or a combination of these, can create the conditions needed to allow an explosion. Only a faulty device can explode: one where either the manufacturer ignored safety features in an attempt to reduce costs, or perhaps believed that small gas vents would suffice, or the small vents were somehow blocked. Keeping costs down and/or minimizing safety features for reasons unknown does not help someone who loses an eye, and it does not help vaping when the explosion is widely reported in the media.

    At first our warnings will only be directed at buyers of metal tubemods that can take two batteries (either by design or by misuse).

    Safe or unsafe models
    We have been requested, by APV manufacturers, to give a safety rating for their products. If the product complies with the above feature set then we would regard it as safe. If it does not comply with the above requirements, no matter what other protections it may have, it does not satisfy our requirements for recognition as safe.

    This does not mean that an incident cannot occur; and it does not mean that minor injuries such as a burnt hand will not happen; it simply means we think it unlikely that an explosion is possible. All we are interested in doing at this point is preventing explosions in front of the face, because this is an achievable goal - other goals may be much harder to achieve.


    [1] A stainless perforated tube appears to be a good start for pressure testing experiments as it will look good and should perform acceptably well. For example, this sort of material could be trialled: www. perforatedtubes .com

    [2] The reasons why an internal sleeve is a good feature are:
    • It prevents an additional negative path being created at a point on the battery case that may have undesirable electrical results within the cell
    • It prevents the negative circuit bypassing a fuse such as a collapsible spring
    There is no suggestion that a direct short-circuit to positive could occur, this seems unlikely (although anything is possible given enough time and variations in circumstances). An insulating sleeve is used for the reasons above, not to prevent a short to positive. Because it is an excellent design feature, it could be a good idea to design new models with a slightly larger tube size to allow for this internal sleeve. Also, sleeves of different thicknesses could be supplied, for example to use smaller cells when necessary (18xxx >> 17xxx >> 16xxx).

    Danger of reverse battery polarity
    It is worth noting that if a battery is inserted in reverse (negative end in first), then there is a serious fault condition waiting to occur if the battery casing shorts out to the device body: battery negative direct to positive. For this reason a battery must NEVER under any circumstances be inserted in reverse, even if the device still works with a reversed circuit direction.


    Manufacturer's information

    Slots and battery wrapper damage
    There is a possibility that milled slots will increase the likelihood of battery cover damage, as the inside edges may be sharp. Careful attention to detail is required here, to break the edges internally. Alternatively, fitting an internal sleeve may fix the problem. The sleeve will need to be perforated or slotted to allow any gas to vent.

    Internal sleeving
    Thin mylar sheet insulates and is tough. It can be used where space is tight, or it might just require the tube I.D. bored or reamed a little larger. It is easily cut to size and slotted.

    mylar info:

    Mylar sheet custom cut, 0.020" thick:

    thin sheet:

    Slot filling
    There have been several suggestions for how to fix the issue of foreign objects or water getting in the slots. This is good progress. Suggestions include: use a filler, with small gaps left; internal sleeve; external sleeve (transparent like a clear plastic coating, or with graphics). It is probable that a plastic filler material can be used such as PU.

    Update 2012-07: an APV model is now available where the gas vent slots have been filled by solid plastic plugs, and the device is reported to be waterproof to IP65. This shows that a solution to water ingress is achievable. In addition the device looks good.

    EMSS implementation and alternatives
    Implementation of the Safety Specification is advised by early June 2012, when we will begin widescale publication and promotion of the guidelines. Alternatively, if not implementing EMSS, you may want to provide suitable information for prospective purchasers as to why your product does not need to comply.


    Update history

    All new versions of EMSS supersede the previous version.
    We introduced the first warnings and advice exactly two years ago in March 2010.

    The first EMSS version, v1, has been in existence for more than one year. Experience and a great deal more data has allowed us to upgrade it to the current version, and it is likely that updates will be a feature of this safety process. From v2 onward, all existing mods that comply with EMSS v2 or later will have protection from obsolescence for a minimum of one year. Please enquire in the Suppliers Forum in the appropriate thread for further details.

    Added note on successful slot filling.

    Added note on gas vents that pressure relief is advisable at the top and bottom of tube.

    Added note regarding info sheet / manual advised for APVs.
    Updated page to change most references from 'mod' to APV.

    Added allowed and disallowed descriptions for a compliant mod.

    Added new paragraph to point out our warnings are 2 years old, and EMSS is now 1 year old, and neither the warnings nor the guidelines are new.

    New design exemption added to Exceptions.

    Intro expanded to include more background.
    Exceptions section added (some design types have a genuine reason for exemption from some part of the EMSS spec.).

    Intro paragraph rewritten to clarify the current status of EMSS.
    Description of gas vent slots expanded to ensure that, until a drawing is available, it is impossible to misunderstand the intention of the slot design and description.

    Updated to clarify that only 2-cell metal tube mods are involved, not those that can only accept 1 cell.


  2. rolygate

    rolygate Forum Manager Verified Member ECF Veteran

    Supporting member
    Sep 24, 2009
    ECF Towers
    Please complete this form if you have a gas vent incident (battery failure event) in an APV (mod) to report. We need this information, and it will be kept confidential.

    The report form is ONLY for APVs - that is, e-cigarette devices with removable batteries.

    Your help is much appreciated.
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